package com.lagou.sqlSession;

import com.lagou.pojo.Configuration;
import com.lagou.pojo.MappedStatement;

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Proxy;
import java.lang.reflect.Type;
import java.util.List;

/**
 * @author mcl
 * @date 2021/6/6 1:15 上午
 * @description
 */
public class DefaultSqlSession implements SqlSession{
    private Configuration configuration;

    public DefaultSqlSession(Configuration configuration) {
        this.configuration = configuration;
    }

    @Override
    public <E> List<E> selectList(String statementId, Object... params) throws Exception {
        // 完成对simpleExecutor里面的query方法的调用
        SimpleExecutor simpleExecutor = new SimpleExecutor();
        MappedStatement mappedStatement = configuration.getMappedStatementMap().get(statementId);
        List<Object> list = simpleExecutor.query(configuration, mappedStatement, params);
        return (List<E>) list;
    }

    @Override
    public <T> T selectOne(String statementId, Object... params) throws Exception {
        List<Object> objects = selectList(statementId, params);
        if (objects.size() == 1) {
            return (T) objects.get(0);
        } else {
            throw new RuntimeException("查询结果为空或者返回结果过多");
        }
    }

    @Override
    public boolean execute(String statementId,Object... param) throws Exception {
        SimpleExecutor simpleExecutor = new SimpleExecutor();
        MappedStatement mappedStatement = configuration.getMappedStatementMap().get(statementId);
        return simpleExecutor.execute(configuration,mappedStatement,param);
    }

    @Override
    public <T> T getMapper(Class<?> mapperClass) {

        // 使用JDK动态代理来为Dao接口生成代理对象，并返回
        Object proxyInstance = Proxy.newProxyInstance(DefaultSqlSession.class.getClassLoader(),
                new Class[]{mapperClass},
                new InvocationHandler() {
                    /**
                     * @param proxy 当前代理对象的应用
                     * @param method 当前被调用方法的引用
                     * @param args 传递的参数
                     * @return
                     * @throws Throwable
                     */
                    @Override
                    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {

                        // 方法名: findAll
                        String methodName = method.getName();
                        String className = method.getDeclaringClass().getName();
                        String statementId = className + "." + methodName;

                        // 准备参数: params: args
                        Type genericReturnType = method.getGenericReturnType();
                        // 判断是否进行来 泛型类型参数化
                        if (genericReturnType instanceof ParameterizedType) {
                            List<Object> objects = selectList(statementId, args);
                            return objects;
                        } else if ("save".equals(methodName) || "update".equals(methodName) || "delete".equals(methodName)) {
                            return execute(statementId, args);
                        }
                        return selectOne(statementId, args);
                    }
                });
        return (T) proxyInstance;
    }
}
